Many youth find television, videos and computer games to be very reinforcing, and they choose to be sedentary rather than physically active. Sedentary behaviors can influence energy balance and body weight by reducing physical activity and increasing energy intake. Research from our laboratory has shown that reducing sedentary behavior can increase physical activity and decrease energy intake, but there is substantial variability in the response of youth to reductions in sedentary behavior. The present proposal is designed to extend our research and explore theoretical models that may help understand why youth vary in their response to increase physical activity when targeted sedentary behaviors are reduced. We hypothesize that the increase in physical activity when sedentary behaviors are reduced is related to the relative reinforcing value (RRV) of physical activity to sedentary behaviors. The RRV of physical activity is a measure of the motivation to be active in youth, and overweight youth who are inactive find physical activity relatively less reinforcing than less overweight youth. We predict that RRV of physical activity will be positively related to the substitution of total physical activity and physical activity in the moderate to vigorous intensity range for sedentary behaviors when targeted sedentary behaviors are reduced. To test this hypothesis, we will study 60 overweight and at risk for overweight 8-12 year-old youth who differ in the RRV of physical activity to sedentary behavior, with equal numbers of boys and girls, in 3 phases: baseline, and reduce television watching from baseline by 25 percent and 50 percent. Each phase will be implemented for three weeks. Order of experimental phases will be counterbalanced across subjects. It is also predicted that reducing sedentary behavior will reduce energy intake and dietary fat intake, and the reduction in energy intake will be greatest for youth with stronger association between eating with television watching and other targeted sedentary behaviors. Liking and outcome expectancy of physical activity will be studied as additional predictors of substitution of physical activity for reductions in sedentary behaviors. Developing a better understanding of why obese youth increase physical activity or decrease energy intake when sedentary behaviors are reduced is important for the treatment of pediatric obesity. [unreadable] [unreadable] [unreadable]